Wireless communication apparatus and wireless communication system

ABSTRACT

A data transmission apparatus transmits data signals “S1” and “S2” containing identical serial data “ds” in two frequency bands, and a data reception apparatus receives those data signals “S1” and “S2.” Parallel data “dpl” and “dpl2” obtained from the data signals “S1” and “S2” is subjected to selection or synthesis in a subcarrier selection/demodulation circuit so as to be demodulated into serial data “dsx,” which is then outputted to a MAC section.

[0001] This nonprovisional application claims priority under 35 U.S.C. §119(a) on patent application Ser. No. 2003-110409 filed in Japan on Apr.15, 2004, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a wireless communicationapparatus and a wireless communication system for performing wirelesscommunication. More particularly, the present invention relates to awireless communication apparatus and a wireless communication systemthat employ a multiple-carrier transmission method such as the OFDM(orthogonal frequency division multiplexing) method for transmitting AVstreams and data on a wireless basis.

[0004] 2. Description of the Prior Art

[0005] In recent years, as methods for transmitting data and AV streamson a wireless basis, among others, those complying with IEEE802.11b,using the 2.4 GHz band, and IEEE802.11a, using the 5.2 GHz band, havebeen becoming increasingly popular. Radio waves in the 2.4 GHz band tendto propagate less rectilinearly than those in the 5.2 GHz band, and thisgives the former the advantage of readily propagating around the cornersof a shielding object and the advantage of offering longer wirelesstransmission distances. However, the 2.4 GHz frequency band is usedcomparatively freely, and is shared by other communication methods suchas Bluetooth and by the radio waves emitted from microwave ovens. Thus,in the 2.4 GHz frequency band, interference with such other microwavestends to lower the effective throughput of communication.

[0006] Accordingly, in a case where the method complying withIEEE802.11b is used for data transmission such as file transfer in awireless LAN (local area network), it is not absolutely necessary toguarantee any specific QoS (quality of service), i.e., to give aguarantee that a particular amount of data is transmitted within aparticular length of time. Thus, interference with unrelated radio wavesdoes not cause any problem. However, in a case where high-quality imagesand sounds are transmitted on a wireless basis, it is necessary toguarantee a certain QoS, and therefore interference with unrelated radiowaves causes an unacceptable lowering of the effective throughput.

[0007] By contrast, the method complying with IEEE802.11a, which usesthe 5.2 GHz band, adopts the OFDM method, and, by using a plurality ofsubcarriers spread over a wide frequency band, achieves a high physicaltransmission rate and a high effective throughput. Thus, this methodcreates a transmission state that offers efficiency high enough toguarantee a desired QoS. However, radio waves in the 5.2 GHz band tendto propagate more rectilinearly than those in the 2.4 GHz band, and thisgives the former the disadvantage of less readily propagating around thecorners of a shielding object and the disadvantage of offering shorterwireless transmission distances. Thus, in wireless transmissionperformed over a wide frequency band, when frequency-selective fadingoccurs due to factors in the indoor or outdoor transmission environment,reception condition may become poor with particular subcarriers only,resulting in the missing of the data transmitted by those subcarriers.

[0008] To prevent such missing of the data carried by a particularsubcarrier, there has been conventionally proposed a diversity receiverwherein reception is achieved by the use of a plurality of antennas and,for each subcarrier, the signals received via the different antennas arecorrected and then synthesized together, or a diversity receiverwherein, for each subcarrier, the signal strengths or the like of thesignals received via a plurality of antennas are compared with oneanother so that a signal being received in good reception condition isselected and demodulated (see Japanese Patent Application Laid-Open No.2000-36801). There has also been conventionally proposed a diversityreceiver wherein a plurality of antennas are used and, for eachsubcarrier, the carrier levels of the signals received via the differentantennas are checked so that a signal being received in good receptioncondition is selected (see Japanese Patent Application Laid-Open No.2000-174726).

[0009] Thus, for example, in a case where the frequency band used is the5.2 GHz band as with the method complying with IEEE802.11a, by using thediversity receiver proposed in one of the patent publications mentionedabove, it is possible to receive OFDM signals via a plurality ofantennas. Here, an attempt is made to prevent the deterioration ofsubcarriers by exploiting the differences in characteristics of thefrequency-selective fading occurring in the individual OFDM signalsreceived by the different antennas.

[0010] However, the diversity receivers proposed in the Japanese PatentApplications Laid-Open Nos. 2000-36801 and 2000-174726 mentioned aboveuse only one frequency band, and therefore, when the plurality ofantennas are arranged close to one another spatially, the signalsreceived by the different antennas may show similar frequency-selectivefading characteristics. In that case, the subcarriers of an identicalfrequency obtained from the OFDM signals received via those antennasexhibit similar degrees of deterioration. Thus, the result of synthesisof those subcarriers, or the result of comparison among and selectionfrom them, may be less accurate than the results for other subcarriers.

[0011] In particular, in a case where OFDM signals in the 5.2 GHz bandare received, when the plurality of antennas are arranged close to oneanother spatially, all the relevant radio waves may fail to propagatearound in similar manners with respect to the different antennas, or mayfail to reach the antennas due to the transmission loss that the radiowaves in that frequency band inevitably suffer along the spatialtransmission paths. This results in poor reception condition via all theantennas.

SUMMARY OF THE INVENTION

[0012] An object of the present invention is to provide a wirelesscommunication apparatus that reduces the influence offrequency-selective fading by receiving an identical signal in aplurality of frequency bands and then synthesizing together or selectingfrom the signals received in the different frequency bands according totheir respective reception condition. Another object of the presentinvention is to provide a wireless communication system built aroundsuch a wireless communication apparatus.

[0013] To achieve the above objects, according to one aspect of thepresent invention, a wireless communication apparatus is provided with:a modulation circuit that generates a plurality of data signalscontaining identical data each in one of a plurality of carrierfrequency bands; and a plurality of antennas via which the plurality ofdata signals outputted from the modulation circuit are transmitted eachin a corresponding one of the plurality of carrier frequency bands.

[0014] According to another aspect of the present invention, a wirelesscommunication apparatus is provided with: a plurality of antennas viawhich are received data signals each transmitted in one of a pluralityof carrier frequency bands; a plurality of frequency conversion circuitsthat convert the data signals received respectively via the plurality ofantennas into a plurality of baseband signals having an identicalfrequency; and a demodulation circuit that, based on the plurality ofbaseband signals obtained respectively from the plurality of frequencyconversion circuits, checks reception condition in the carrier frequencybands corresponding respectively to the plurality of data signals andselects the baseband signal obtained from the data signal in the carrierfrequency band in which reception condition is found best and that thendemodulates the thus selected baseband signal. Here, the data signalstransmitted respectively in the plurality of carrier frequency bandscontain identical data.

[0015] According to another aspect of the present invention, a wirelesscommunication apparatus is provided with: a plurality of antennas viawhich are received data signals each transmitted in one of a pluralityof carrier frequency bands; a plurality of frequency conversion circuitsthat convert the data signals received respectively via the plurality ofantennas into a plurality of baseband signals having an identicalfrequency; and a demodulation circuit that synthesizes together theplurality of baseband signals obtained respectively from the pluralityof frequency conversion circuits into a single baseband signal and thatthen demodulates the thus synthesized baseband signal. Here, the datasignals transmitted respectively in the plurality of carrier frequencybands contain identical data.

[0016] According to another aspect of the present invention, a wirelesscommunication apparatus is provided with: n (where n is an integer equalto or greater than 2) antennas via which are received data signalsmodulated by an OFDM modulation method and transmitted in n carrierfrequency bands; n frequency conversion circuits that convert the datasignals received respectively via the n antennas into baseband signalshaving an identical frequency; n Fourier transform circuits that, basedon the plurality of baseband signals obtained respectively from the nfrequency conversion circuits, generate parallel data containing datasegments each relating to one of m (where m is an integer equal to orgreater than 2) subcarriers; n data correction circuits that, based onthe parallel data fed respectively from the n Fourier transformcircuits, check reception condition of each of the m subcarriers in therespective carrier frequency bands and accordingly correct the paralleldata; a data selection circuit that receives the n sets of parallel datacorrected by the n data correction circuits and that then, for each ofthe m subcarriers, recognizes the carrier frequency band in whichreception condition is best and that then selects the data in the thusrecognized carrier frequency band so as to thereby newly generateparallel data containing m data segments; and a demodulation circuitthat converts the parallel data newly generated by the data selectioncircuit into serial data. Here, the parallel data contained in the datasignals transmitted respectively in the plurality of carrier frequencybands contains identical data.

[0017] According to another aspect of the present invention, a wirelesscommunication apparatus is provided with: n (where n is an integer equalto or greater than 2) antennas via which are received data signalsmodulated by an OFDM modulation method and transmitted in n carrierfrequency bands; n frequency conversion circuits that convert the datasignals received respectively via the n antennas into baseband signalshaving an identical frequency; n Fourier transform circuits that, basedon the plurality of baseband signals obtained respectively from the nfrequency conversion circuits, generate parallel data containing datasegments each relating to one of m (where m is an integer equal to orgreater than 2) subcarriers; n data correction circuits that, based onthe parallel data fed respectively from the n Fourier transformcircuits, check reception condition of each of the m subcarriers in therespective carrier frequency bands and accordingly correct the paralleldata; a data synthesis circuit that receives the n sets of parallel datacorrected by the n data correction circuits and that then, for each ofthe m subcarriers, synthesizes the data so as to thereby newly generateparallel data containing m data segments; and a demodulation circuitthat converts the parallel data newly generated by the data synthesiscircuit into serial data. Here, the parallel data contained in the datasignals transmitted respectively in the plurality of carrier frequencybands contains identical data.

[0018] According to another aspect of the present invention, a wirelesscommunication apparatus is provided with: n (where n is an integer equalto or greater than 2) antennas via which are received data signalsmodulated by an OFDM modulation method and transmitted in n carrierfrequency bands; n frequency conversion circuits that convert the datasignals received respectively via the n antennas into baseband signalshaving an identical frequency; n Fourier transform circuits that, basedon the plurality of baseband signals obtained respectively from the nfrequency conversion circuits, generate parallel data containing datasegments each relating to one of m (where m is an integer equal to orgreater than 2) subcarriers; a data selection circuit that receives then sets of parallel data obtained from the n Fourier transform circuitsand that then, for each of the m subcarriers, recognizes the carrierfrequency band in which reception condition is best and that thenselects the data in the thus recognized carrier frequency band so as tothereby newly generate parallel data containing m data segments; a datacorrection circuit that, based on the parallel data newly generated bythe data selection circuit, checks reception condition of each of the msubcarriers in the respective carrier frequency bands and accordinglycorrect the parallel data; and a demodulation circuit that converts theparallel data corrected by the data correction circuit into serial data.Here, the parallel data contained in the data signals transmittedrespectively in the plurality of carrier frequency bands containsidentical data.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] This and other objects and features of the present invention willbecome clear from the following description, taken in conjunction withthe preferred embodiments with reference to the accompanying drawings inwhich:

[0020]FIG. 1 is a block diagram showing the configuration of a wirelesscommunication system according to the present invention;

[0021]FIG. 2 is a block diagram showing the configuration of the datareception apparatus of a first embodiment of the invention;

[0022]FIGS. 3A and 3B are diagrams illustrating the operation of thedata correction circuit;

[0023]FIG. 4 is a diagram illustrating the operation of the dataselection circuit;

[0024]FIG. 5 is a block diagram showing the configuration of the datareception apparatus of a second embodiment of the invention;

[0025]FIG. 6 is a diagram illustrating the operation of the datasynthesis circuit;

[0026]FIG. 7 is a block diagram showing the configuration of the datareception apparatus of a third embodiment of the invention;

[0027]FIG. 8 is a block diagram showing the configuration of the datareception apparatus of a fourth embodiment of the invention;

[0028]FIG. 9 is a block diagram showing another example of theconfiguration of the data reception apparatus of the fourth embodiment;

[0029]FIG. 10 is a block diagram showing still another example of theconfiguration of the data reception apparatus of the fourth embodiment;

[0030]FIG. 11 is a block diagram showing the configuration of the datareception apparatus of a fifth embodiment of the invention;

[0031]FIG. 12 is a block diagram showing another example of theconfiguration of the data reception apparatus of the fifth embodiment;and

[0032]FIG. 13 is a block diagram showing still another example of theconfiguration of the data reception apparatus of the fifth embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Basic Configuration

[0034] The basic configuration according to the present invention willbe described below with reference to the drawings. FIG. 1 is a blockdiagram showing the configuration of a wireless communication systemaccording to the invention. The wireless communication system shown inFIG. 1 is provided with: a data transmission apparatus 1 that modulatesinputted data by the OFDM method and that then transmits the modulateddata; and a data reception apparatus 2 that receives the data signaltransmitted from the data transmission apparatus 1 and that then outputsthe data obtained by demodulating the data signal by the OFDM method.This wireless communication system composed of the data transmissionapparatus 1 and the data reception apparatus 2 use two frequency bands,namely the 2.4 GHz and 5.2 GHz bands, and identical data signals aretransmitted in both the 2.4 GHz and 5.2 GHz frequency bands.

[0035] In this wireless communication system, the data transmissionapparatus 1 is provided with: an interleave circuit 10 that generatesparallel data by dividing inputted serial data into segments of data ofwhich the number is equal to the number of subcarriers; a mappingcircuit 11 that performs mapping in a fashion conforming to the QAM(quadratic amplitude modulation), QPSK (quadruple phase shift keying),or other method; an inverse Fourier transform circuit 12 that performsinverse Fourier transform on the parallel data generated by the mappingcircuit 11; a parallel-to-serial conversion circuit 13 that synthesizestogether the parallel data subjected to inverse Fourier transform by theinverse Fourier transform circuit 12 to generate two quadrature signalscalled an I and a Q signal; a quadrature modulation circuit 14 thatperforms quadrature modulation on the I and Q signals from theparallel-to-serial conversion circuit 13 to generate a baseband signal;an RF circuit 15 a that performs frequency conversion on the basebandsignal from the quadrature modulation circuit 14 to convert it into ahigh-frequency signal in the 2.4 GHz band; an RF circuit 15 b thatperforms frequency conversion on the baseband signal from the quadraturemodulation circuit 14 to convert it into a high-frequency signal in the5.2 GHz band; and antennas 16 a and 16 b via which the high-frequencysignals from the RF circuits 15 a and 15 b are transmitted.

[0036] On the other hand, the data reception apparatus 2 is providedwith: antennas 21 a and 21 b via which high-frequency signals in the 2.4GHz and 5.2 GHz, respectively, are received; RF circuits 22 a and 22 bthat perform frequency conversion on the high-frequency signals receivedvia the antennas 21 a and 21 b, respectively, to convert them intobaseband signals; quadrature detection circuits 23 a and 23 b thatperform quadrature detection on the baseband signals from the RFcircuits 22 a and 22 b, respectively, by using two local oscillationsignals 90° out of phase with each other to produce an I and a Q signal;serial-to-parallel conversion circuits 24 a and 24 b that generateparallel data from the I and Q signals from the quadrature detectioncircuits 23 a and 23 b; Fourier transform circuits 25 a and 25 b thatperform fast Fourier transform on the parallel data obtained from theserial-to-parallel conversion circuits 24 a and 24 b; a subcarrierselection/demodulation circuit 26 that receives the parallel datasubjected to Fourier transform by the Fourier transform circuit 25 a and25 b, respectively, and that then, for each subcarrier, selects data ingood condition in order to generate serial data from the thus selectedparallel data; and a MAC section 50 that checks the MAC (medial accesscontrol) frames in the serial data from the subcarrierselection/demodulation circuit 26 to perform synchronism control andother operations.

[0037] Configured as described above, the data transmission apparatus 1and the data reception apparatus 2 operate as follows. First, in thedata transmission apparatus 1, the interleave circuit 10 generatesparallel data “dp” by dividing serial data “ds” into segments of data ofwhich the number is equal to the number of subcarriers in such a waythat no temporally consecutive parts of the data are allotted toadjacent subcarriers. Then, the mapping circuit 11 modulatesindividually the segments of the parallel data “dp” allotted to thedifferent subcarriers in a fashion conforming to the QAM, QPSK, or othermethod. Thereafter, the parallel data “dp” modulated by the mappingcircuit 11 is subjected to inverse Fourier transform performed by theinverse Fourier transform circuit 12. The parallel data “dp” is then fedto the parallel-to-serial conversion circuit 13 so as to be convertedinto two signals, namely an I signal “si” and a Q signal “sq,” which arethen subjected to quadrature modulation by the quadrature modulationcircuit 14 so as to be converted into a single signal, namely a basebandsignal “b.”

[0038] This baseband signal “b” is fed to both the RF circuits 15 a and15 b, which thus generate high-frequency signals “S1” and “S2,”respectively, containing the same data. These high-frequency signals“S1” and “S2” are then transmitted via the antenna 16 a and 16 b intheir respective carrier frequency bands, namely the 2.4 GHz and 5.2 GHzbands. In this way, two high-frequency signals “S1” and “S2” generatedfrom identical serial data “ds” are transmitted in the 2.4 GHz and 5.2GHz carrier frequency bands, respectively.

[0039] Then, in the data reception apparatus 2, the high-frequencysignal “S1” transmitted in the 2.4 GHz carrier frequency band isreceived via the antenna 21 a, and the high-frequency signal “S2”transmitted in the 5.2 GHz carrier frequency band is received via theantenna 21 b. The high-frequency signal “S1” received via the antenna 21a is converted by the RF circuit 22 a into a baseband signal “b1,” whichis then converted by the quadrature detection circuit 23 a into an Isignal “si1” and a Q signal “sq1.” The I and Q signals “si1” and “sq1”originating from the high-frequency signal “S1” are fed to theserial-to-parallel conversion circuit 24 a so as to be converted intoparallel data “dp1” containing different segments of data for differentsubcarriers, and then this parallel data “dp1” is subjected to Fouriertransform performed by the Fourier transform circuit 25 a.

[0040] On the other hand, the high-frequency signal “S2” received viathe antenna 21 b is converted by the RF circuit 22 b into a basebandsignal “b2” having the same frequency as the baseband signal “b1,” andthis baseband signal “b2” is then converted by the quadrature detectioncircuit 23 b into an I signal “si2” and a Q signal “sq2.” The I and Qsignals “si2” and “sq2” originating from the high-frequency signal “S2”are fed to the serial-to-parallel conversion circuit 24 b so as to beconverted into parallel data “dp2” containing different segments of datafor different subcarriers, and then this parallel data “dp2” issubjected to Fourier transform performed by the Fourier transformcircuit 25 b.

[0041] The parallel data “dp1” and “dp2” subjected to Fourier transformby the Fourier transform circuits 25 a and 25 b, respectively, is thenfed to the subcarrier selection/demodulation circuit 26. With respect tothe parallel data “dp1” and “dp2” obtained by receiving thehigh-frequency signals “S1” and “S2” generated from the identical serialdata “ds,” the subcarrier selection/demodulation circuit 26 firstcorrects those data for the influence of their respective transmissionpaths on the basis of the reception condition of the individualsubcarriers, and then either selects from or synthesize together, foreach subcarrier, the corresponding segments contained in the paralleldata “dp1” and “dp2.”

[0042] Specifically, in a case where data received in good condition isselected, for example, when the parallel data “dp1” is received in goodcondition in a subcarrier having a frequency “fx” and the parallel data“dp2” is received in good condition in a subcarrier having a frequency“fy,” as the data of the subcarrier having the frequency “fx” is usedthat contained in the parallel data “dp1,” and as the data of thesubcarrier having the frequency “fy” is used that contained in theparallel data “dp2.” In a case where data is synthesized, for eachsubcarrier, the corresponding segments are synthesized togetheraccording to their values. Then, the parallel data “dpx” obtainedthrough selection or synthesis performed for each subcarrier isconverted into serial data “dsx” containing less errors, and this serialdata “dsx” is outputted to the MAC section 50.

[0043] The embodiments described hereinafter all deal with a wirelesscommunication system of which the basic configuration is as shown inFIG. 1. In all the embodiments, the data transmission apparatus 1 hasthe same configuration. Accordingly, in the following descriptions ofthe individual embodiments, the configuration of the data receptionapparatus 2 will mainly be discussed, with emphasis placed on itssubcarrier selection/demodulation circuit 26, whose configuration variesfrom one embodiment to another.

FIRST EMBODIMENT

[0044] A first embodiment of the invention will be described below withreference to the drawings. FIG. 2 is a block diagram showing theinternal configuration of the data reception apparatus used in thewireless communication system of this embodiment.

[0045] In the data reception apparatus 2 a shown in FIG. 2(corresponding to the data reception apparatus 2 shown in FIG. 1), thesubcarrier selection/demodulation circuit 26 a (corresponding to thesubcarrier selection/demodulation circuit 26 shown in FIG. 1) isprovided with: channel evaluation circuits 27 a and 27 b that predict,for each subcarrier, the influence of the transmission path of thecorresponding frequency channel on the parallel data “dp1” and “dp2” fedrespectively from the Fourier transform circuits 25 a and 25 b and thatthen generate influence correction information for correcting for theinfluence of the transmission path; channel correction circuits 28 a and28 b that correct the parallel data “dp1” and “dp2” fed respectivelyfrom the Fourier transform circuits 25 a and 25 b for the influence ofthe transmission path of the subcarrier channel on the basis of theinfluence correction information from the channel evaluation circuits 27a and 27 b; a data selection circuit 29 that compares, for eachsubcarrier, the parallel data “dp1” and “dp2” for which the subcarriersare corrected by the channel correction circuits 28 a and 28 b in orderto select the subcarriers being received in good condition and therebynewly generate parallel data “dpx”; and a de-mapping circuit 30 thatperforms, for each subcarrier, de-mapping on the parallel data “dpx”selected by the data selection circuit 29 in a fashion conforming to theQAM, QPSK, or other method; and a de-interleave circuit 31 thatgenerates serial data “dsx” from the parallel data “dpx” demodulated bythe de-mapping circuit 30.

[0046] Configured as described above, the data reception apparatus 2 aoperates as follows. As described earlier in connection with the basicconfiguration, the data reception apparatus 2 a receives via the antenna21 a the high-frequency signal “S1” transmitted in the 2.4 GHz carrierfrequency band, and receives via the antenna 21 b the high-frequencysignal “S2” transmitted in the 5.2 GHz carrier frequency band.Thereafter, the high-frequency signal “S1” received via the antenna 21 ais, through the RF circuit 22 a, quadrature detection circuit 23 a,serial-to-parallel conversion circuit 24 a, and Fourier transformcircuit 25 a, converted into parallel data “dp1,” which is then fed tothe subcarrier selection/demodulation circuit 26 a. On the other hand,the high-frequency signal “S2” received via the antenna 21 b is, throughthe RF circuit 22 b, quadrature detection circuit 23 b,serial-to-parallel conversion circuit 24 b, and Fourier transformcircuit 25 b, converted into parallel data “dp2,” which is then fed tothe subcarrier selection/demodulation circuit 26 a.

[0047] In the subcarrier selection/demodulation circuit 26 a, theparallel data “dp1” from the Fourier transform circuit 25 a is fed tothe channel evaluation circuit 27 a and the channel correction circuit28 a, and the parallel data “dp2” from the Fourier transform circuit 25b is fed to the channel evaluation circuit 27 b and the channelcorrection circuit 28 b. The channel evaluation circuit 27 a checks, foreach subcarrier, the data contained in the parallel data “dp1” andthereby checks the transmission state of each subcarrier channel in the2.4 GHz band, and the channel evaluation circuit 27 b checks, for eachsubcarrier, the data contained in the parallel data “dp2” and therebychecks the transmitting state of each subcarrier channel in the 5.2 GHzband.

[0048] Here, let us assume that there are 48 subcarrier channels, andthe parallel data “dp1” and “dp2” contains, as data for the individualsubcarrier channels, data segments “dp1-1” to “dp1-48” and “dp2-1” to“dp2-48,” respectively. Let us assume also that, in addition to thesubcarriers, there are four pilot carriers, and, for the parallel data“dp1” and “dp2,” pilot carrier data segments “p1-1” to “p1-4” and “p2-1”to “p2-4,38 respectively, are obtained.

[0049] With the parallel data “dp1” and “dp2” configured as describedabove, when the parallel data “dp1” is fed to the channel evaluationcircuit 27 a, the channel evaluation circuit 27 a compares each of thedata segments “dp1-1” to “dp1-48” with whichever of the pilot carrierdata segments “p1-1” to “p1-4” is selected as being close to thecorresponding sub carrier channel. Specifically, for the data segment“dp-m” (1≦m≦48), the pilot carrier “p1-x” (1≦x≦4) closest to thecorresponding subcarrier channel is selected. Then, the data segment“dp-m” is compared with the pilot carrier “p1-x.”

[0050] At this time, constellation information is also checked for eachof the subcarrier channel data segments “dp1-1” to “dp1-48.” Here,constellation information denotes the values of the phase and amplitudewith which is modulated the subcarrier and to which is allocated eachcode corresponding to the data corresponding to the subcarrier, and isgiven as a point on a two-dimensional coordinate system with one axisrepresenting the in-phase component (I signal) and the other thequadrature component (Q signal). Specifically, when the individualsubcarrier data segments are modulated by the 16 QAM method, theconstellation information of each subcarrier channel, when receivednormally, is as shown in FIG. 3A.

[0051] As a result of, with respect to each of the subcarrier channeldata segments “dp1-1” to “dp1-48,” constellation information beingchecked and comparison being made with the pilot carrier “p1-x” closethereto in this way, the reception condition of the individualsubcarrier channels is recognized. On the basis of the thus recognizedreception condition, deviations in the phase of the individualsubcarriers and deviations in the amplitude thereof resulting fromvariations in reception signal strength are recognized, and influencecorrection information for correcting for those deviations in the phaseand amplitude is generated for each of the data segments “dp1-1” to“dp1-48.”

[0052] Specifically, for example, suppose that, when the receptioncondition of the subcarrier channel of the data segment “dp-m” ischecked, the constellation information of the data segment “dp-m” isfound to be represented as shown in FIG. 3B. In this case, as comparedwith when reception is normal as shown in FIG. 3A, it is recognized thatthe phase deviates by θ, and that the amplitude is 1/X times theamplitude B obtained when reception is normal. Accordingly, theinfluence correction information for the data segment “dp-m” isinformation that requests that, for the data segment “dp-m,” the phasebe rotated by −θ and the amplitude be multiplied by X.

[0053] Likewise, in the channel evaluation circuit 27 b, as in thechannel evaluation circuit 27 a, when the parallel data “dp2” is fedthereto, the channel evaluation circuit 27 b compares each of the datasegments “dp2-1” to “dp2-48” with whichever of the pilot carrier datasegments “p2-1” to “p2-4” is selected as being close thereto, and cheeksconstellation information for each of the data segments “dp2-1” to“dp2-48” and thereby checks the reception condition of the individualsubcarrier channels in the 5.2 GHz. After the reception condition of theindividual subcarrier channels is checked, on the basis of the receptioncondition thus recognized, influence correction information is generatedfor each of the data segments “dp2-1” to “dp2-48.”

[0054] The influence correction information thus generated by thechannel evaluation circuits 27 a and 27 b is then fed to the channelcorrection circuits 28 a and 28 b, respectively. Thus, the channelcorrection circuit 28 a corrects the individual data segments “dp1-1” to“dp1-48” on the basis of the influence correction information generatedrespectively for those data segments “dp1-1” to “dp1-48” by the channelevaluation circuit 27 a. Specifically, with respect to the data segment“dp1-m” of which the constellation information is as shown in FIG. 3B,the phase is rotated by −θ and the amplitude is multiplied by X so thatthe data segment is corrected to one that gives a value close to theconstellation information obtained when reception is normal as shown inFIG. 3A. Likewise, the channel correction circuit 28 b corrects theindividual data segments “dp2-1” to “dp2-48” on the basis of theinfluence correction information generated respectively for those datasegments “dp2-1” to “d2-48” by the channel evaluation circuit 27 b.

[0055] The parallel data “dp1” and “dp2” thus corrected with respect toeach subcarrier by the channel correction circuits 28 a and 28 b is thenfed to the data selection circuit 29. In the data selection circuit 29,the constellation information for the identical subcarrier in theparallel data “dp1” and “dp2” is checked and compared with theconstellation information obtained when reception is normal. Then, foreach of the subcarrier, the data segment closer to the constellationinformation obtained when reception is normal is selected, and therebynew parallel data “dpx” is generated.

[0056] Here, let us assume that, when the constellation information ofthe data segment “dp1-m” in the parallel data “dp1” and theconstellation information of the data segment “dp2-m” in the paralleldata “dp2” is checked, the corresponding positions on thetwo-dimensional coordinate system that shows signal point locations arepoints α and β in FIG. 4, respectively. Let us assume also that theposition on the two-dimensional coordinate system that shows signalpoint locations as observed when reception is normal is point A. In thiscase, the distance between point A and point a and the distance betweenpoint A and point β are checked and compared.

[0057] When the relation between the distance L1 between positions A andα and the distance L2 between positions A and β is L1>L2, in thetwo-dimensional coordinate system that shows signal point locations, theconstellation information that represents point β is found to be closerto the constellation information that represents point A than theconstellation information that represents point α is. Accordingly, thedata segment “dp2-m” in the parallel data “dp2,” which has theconstellation information that represents point β, is selected as the“dpx-m” of the parallel data “dpx.”

[0058] Likewise, when the constellation information of the data segment“dp1-n” in the parallel data “dp1” and the constellation information ofthe data segment “dp2-n” in the parallel data “dp2” is checked, therelationship between the thus recognized constellation information andthe constellation information obtained when reception is normal ischecked on the two-dimensional coordinate system that shows signal pointlocations and is compared. If, on the two-dimensional coordinate systemthat shows signal point locations, the relationship between theconstellation information of the data segment “dp1-n” in the paralleldata “dp1” and the constellation information obtained when reception isnormal is found to be closer, the data segment “dp1-m” in the paralleldata “dp1” is selected as the “dpx-m” of the parallel data “dpx.”

[0059] In this way, as the data segments “dpx-1” to “dpx-48” in theparallel data “dpx,” whichever of the data segments “dp1-1” to “dp1-48”in the parallel data “dp1” and data segments “dp2-1” to “dp2-48” in theparallel data “dp2” have constellation information closer to thatobtained when reception is normal are selected. Specifically, as thedata segment contained in the parallel data “dpx” as corresponding toeach subcarrier, whichever of the data segments contained in theparallel data “dp1” and “dp2” as corresponding to that subcarrier hasconstellation information closer to that obtained when reception isnormal is selected. Accordingly, which of the parallel data “dp1” and“dp2” is selected differs from one subcarrier to another.

[0060] The parallel data “dpx” thus generated by selecting, for eachsubcarrier, the data segment that has constellation information closerto that obtained when reception is normal is then fed to the de-mappingcircuit 30. The de-mapping circuit 30 performs demodulation for each ofthe subcarrier of the parallel data “dpx” in a fashion conforming to theQAM, QPSK, or other method. Specifically, when the individual subcarrierare modulated by the 16 QAM method, for each of the data segments“dpx-1” to “dpx-48” in the parallel data “dpx,” on the basis of thetwo-dimensional coordinate system that shows signal point locations asshown in FIG. 3A, the four-bit code before being modulation by the datatransmission apparatus 1 is recognized from the relationship of thephase and amplitude of that data segment, and the thus recognizedfour-bit code is demodulated.

[0061] The thus de-mapped parallel data “dpx” is then fed to thede-interleave circuit 31. Here, the codes represented by variations inthe data of the individual subcarrier are connected together along thetemporal axis in the order assigned to those subcarrier so as togenerate serial data “dsx.” That is, as a result of the data segments“dpx-1” to “dpx-48,” each a four-bit code now as described above, beingoutputted in the order assigned respectively thereto from thede-interleave circuit 31, serial data “dsx” consisting of 4×48-bit codesis generated.

[0062] In this embodiment, for the parallel data obtained from twosignals received in two frequency bands, constellation information ischecked for each subcarrier so that constellation information closer tothat obtained when reception is normal is selected. In this way, it ispossible to reduce the influence of frequency-selective fading thataffects the subcarrier individually.

SECOND EMBODIMENT

[0063] A second embodiment of the invention will be described below withreference to the drawings. FIG. 5 is a block diagram showing theinternal configuration of the data reception apparatus used in thewireless communication system of this embodiment. In the data receptionapparatus shown in FIG. 5, such blocks as serve the same purposes as inthe data reception apparatus shown in FIG. 2 are identified with thesame reference numerals, and their detailed explanations will not berepeated.

[0064] In the data reception apparatus 2 b shown in FIG. 5(corresponding to the data reception apparatus 2 shown in FIG. 1), thesubcarrier selection/demodulation circuit 26 b (corresponding to thesubcarrier selection/demodulation circuit 26 shown in FIG. 1) isprovided with, in place of the data selection circuit 29 provided in thesubcarrier selection/demodulation circuit 26 a (FIG. 2), a datasynthesis circuit 29 a that generates parallel data “dpx” bysynthesizing together, for each subcarrier, the parallel data “dp1” and“dp2” of which the individual subcarriers have been corrected by thechannel correction circuits 28 a and 28 b. In other respects, the datareception apparatus 2 b of this embodiment is provided with the sameblocks as those provided in the data reception apparatus 2 a of thefirst embodiment.

[0065] This data reception apparatus 2 b provided with the datasynthesis circuit 29 a in this way operates as follows. First, as in thedata reception apparatus 2 a of the first embodiment, when ahigh-frequency signal “S1” in the 2.4 GHz band and a high-frequencysignal “S2” in the 5.2 GHz band are received via the antennas 21 a and21 b, respectively, they are, through the RF circuits 22 a and 22 b,quadrature detection circuits 23 a and 23 b, serial-to-parallelconversion circuits 24 a and 24 b, and Fourier transform circuits 25 aand 25 b, converted into parallel data “dp1” and “dp2,” which is thenfed to the subcarrier selection/demodulation circuit 26 b.

[0066] In the subcarrier selection/demodulation circuit 26 b, theparallel data “dp1” is fed to the channel evaluation circuit 27 a andthe channel correction circuit 28 a so that the parallel data “dp1” iscorrected with respect to each subcarrier in the channel correctioncircuit 28 a on the basis of the influence correction informationgenerated for each subcarrier in the channel evaluation circuit 27 a. Onthe other hand, the parallel data “dp2” is fed to the channel evaluationcircuit 27 b and the channel correction circuit 28 b so that theparallel data “dp2” is corrected with respect to each subcarrier in thechannel correction circuit 28 b on the basis of the influence correctioninformation generated for each subcarrier in the channel evaluationcircuit 27 b.

[0067] The parallel data “dp1” and “dp2” thus corrected with respect toeach subcarrier is then fed to the data synthesis circuit 29 a. The datasynthesis circuit 29 a then synthesizes the data for the individualsubcarriers on the basis of the constellation information for theidentical subcarrier in the parallel data “dp1” and “dp2.” The operationof this data synthesis circuit 29 a will be described below withreference to FIG. 6. FIG. 6 is a diagram showing the coordinatepositions, on the two-dimensional coordinate system that shows signalpoint locations, recognized from the constellation information of thedata segment “dp1-m” in the parallel data “dp1” and the constellationinformation of the data segment “dp2-m” in the parallel data “dp2.”

[0068] As in FIG. 4, in FIG. 6, let us assume that the positionrecognized from the constellation information of the data segment“dp1-m” in the parallel data “dp1” on the two-dimensional coordinatesystem that shows signal point locations is α, and that the positionrecognized from the constellation information of the data segment“dp2-m” in the parallel data “dp2” on the two-dimensional coordinatesystem that shows signal point locations is β. Let us assume also thatthe position observed when reception is normal on the two-dimensionalcoordinate system that shows signal point locations is point A.

[0069] In this case, the data synthesis circuit 29 a synthesizestogether the constellation information of the data segments “dp1-m” and“dp2-m” to calculate the constellation information corresponding to thecoordinate position of point γ located at the midpoint between points αand β recognized on the two-dimensional coordinate system that showssignal point locations as shown in FIG. 6. Then, the data synthesiscircuit 29 a generates the data segment “dpx-m” in such a way that theconstellation information of the data segment “dpx-m” corresponds to thecoordinate position of point γ. That is, by using the coordinatepositions recognized from the phase and amplitude of the subcarriercorresponding to the data segments “dp1-m” and “dp2-m” as obtained fromthe constellation information of the data segments “dp1-m” and “dp2-m,”the coordinate position located at the midpoint between those coordinatepositions is calculated, then the phase and amplitude of the subcarrierrecognized from that coordinate position is recognized, and then thedata segment dpx-m” is generated from the constellation information thatrepresents those phase and amplitude.

[0070] In this way, as a result of the data segments “dp1-1” to “dp1-48”in the parallel data “dp1” and the data segments “dp2-1” to “dp2-4” inthe parallel data “dp2” being synthesized together, the data segments“dpx-1” to “dpx-48” in the parallel data “dpx” are obtained as datacorresponding to the mid positions between the positions represented bythe data segments “dp1-1” to “dp1-48” in the parallel data “dp1” and thepositions represented by the data segments “dp2-1” to “dp2-48” in theparallel data “dp2.”

[0071] Thus, the data for the individual subcarriers in the paralleldata “dpx” is generated by synthesizing together the data for thosesubcarriers in the parallel data “dp1” and “dp2.” This makes theconstellation information of the individual subcarriers of the paralleldata “dpx” thus obtained through synthesis closer to the constellationinformation obtained when reception is normal. Thereafter, the paralleldata “dpx” is, through the de-mapping circuit 30 and the de-interleavecircuit 31, converted into serial data “dsx,” which is then outputted.

[0072] In this embodiment, the parallel data obtained from two signalsreceived in two frequency bands is synthesized together with respect toeach subcarrier. This makes it possible to make the resultingconstellation information closer to the constellation informationobtained when reception is normal. Thus, it is possible to reduce theinfluence of frequency-selective fading that affects the subcarriersindividually.

[0073] In this embodiment, when the data synthesis circuit generates thedata for the individual subcarriers in the parallel data, for eachsubcarrier, the midpoint coordinate position between the two pointscorresponding to the two signals received in different frequency bandsas observed on the two-dimensional coordinate system that shows signalpoint locations is recognized, and the data corresponding to thatmidpoint coordinate position is used as the data for that subcarrier.However, data synthesis may be achieved in any other manner. Forexample, the data synthesis circuit may be so configured as to generatethe data for the individual subcarriers in the parallel data byevaluating the relationship between the coordinate positions of the twopoints corresponding to the two signals received in different frequencybands and the coordinate position obtained when reception is normal asobserved on the two-dimensional coordinate system that shows signalpoint locations and then adding those points together with appropriateweights given thereto so as to integrate them together.

THIRD EMBODIMENT

[0074] A third embodiment of the invention will be described below withreference to the drawings. FIG. 7 is a block diagram showing theinternal configuration of the data reception apparatus used in thewireless communication system of this embodiment. In the data receptionapparatus shown in FIG. 7, such blocks as serve the same purposes as inthe data reception apparatus shown in FIG. 2 are identified with thesame reference numerals, and their detailed explanations will not berepeated.

[0075] In the data reception apparatus 2 c shown in FIG. 7(corresponding to the data reception apparatus 2 shown in FIG. 1), thesubcarrier selection/demodulation circuit 26 c (corresponding to thesubcarrier selection/demodulation circuit 26 shown in FIG. 1) is soconfigured that the parallel data “dp1” and “dp2” form the Fouriertransform circuits 25 a and 25 b is fed to the data selection circuit29, and is provided with, in place of the channel correction circuits 28a and 28 b, a channel correction circuit 28 that receives the paralleldata “dpx” outputted from the data selection circuit 29. In otherrespects, the data reception apparatus 2 c of this embodiment isprovided with the same blocks as those provided in the data receptionapparatus 2 a (FIG. 2) of the first embodiment.

[0076] Configured as described above, this data reception apparatus 2 coperates as follows. First, as in the data reception apparatus 2 a ofthe first embodiment, a high-frequency signal “S1” in the 2.4 GHz bandand a high-frequency signal “S2” in the 5.2 GHz band received via theantennas 21 a and 21 b are, through the RF circuits 22 a and 22 b,quadrature detection circuits 23 a and 23 b, serial-to-parallelconversion circuits 24 a and 24 b, and Fourier transform circuits 25 aand 25 b, converted into parallel data “dp1” and “dp2,” which is thenfed to the subcarrier selection/demodulation circuit 26 c.

[0077] In the subcarrier selection/demodulation circuit 26 c, thechannel evaluation circuits 27 a and 27 b, which respectively receivethe parallel data “dp1” and “dp2,” generate influence correctioninformation for each subcarrier in the same manner as in the firstembodiment. As opposed to the subcarrier selection/demodulation circuit26 a of the first embodiment, however, here, the data selection circuit29 receives from the Fourier transform circuits 25 a and 25 b theparallel data “dp1” and “dp2” that is not yet corrected with respect toeach subcarrier. The data selection circuit 29 operates in the samemanner as in the first embodiment, and accordingly the data that hasconstellation information closer to that obtained when reception isnormal is selected to generate parallel data “dpx.”

[0078] The parallel data “dpx” thus generated is then fed to the channelcorrection circuit 28. For this parallel data “dpx,” the channelcorrection circuit 28 selects, with respect to each subcarrier,appropriate influence correction information from the channel evaluationcircuits 27 a and 27 b, and then, on the basis of the thus selectedinfluence correction information, performs data correction. Here, forthose subcarriers for which the data in the parallel data “dp1” isselected by the data selection circuit 29, data correction is performedon the basis of the influence correction information from the channelevaluation circuit 27 a, and for those subcarriers for which the data inthe parallel data “dp2” is selected by the data selection circuit 29,data correction is performed on the basis of the influence correctioninformation from the channel evaluation circuit 27 b.

[0079] Here, the data correction operation performed by the channelcorrection circuit 28 is the same as the data correction operationperformed by the channel correction circuits 28 a and 28 b in the firstembodiment. The parallel data “dpx” thus corrected with respect to eachsubcarrier is then, through the de-mapping circuit 30 and thede-interleave circuit 31, converted into serial data “dsx,” which isthen outputted.

FOURTH EMBODIMENT

[0080] A fourth embodiment of the invention will be described below withreference to the drawings. FIG. 8 is a block diagram showing theinternal configuration of the data reception apparatus used in thewireless communication system of this embodiment. In the data receptionapparatus shown in FIG. 8, such blocks as serve the same purposes as inthe data reception apparatus shown in FIG. 2 are identified with thesame reference numerals, and their detailed explanations will not berepeated.

[0081] In the data reception apparatus 2 d shown in FIG. 8(corresponding to the data reception apparatus 2 shown in FIG. 1), thesubcarrier selection/demodulation circuit 26 d (corresponding to thesubcarrier selection/demodulation circuit 26 shown in FIG. 1), ascompared with the subcarrier selection/demodulation circuit 26 a (FIG.2), is additionally provided with: de-mapping circuits 30 a and 30 bthat de-map the parallel data “dp1” and “dp2” of which the individualsubcarriers have been corrected by the channel correction circuits 28 aand 28 b, respectively; de-interleave circuits 31 a and 31 b thatde-interleave the parallel data “dp1” and “dp2” demodulated by thede-mapping circuits 30 a and 30 b; and a selector switch SW that selectsamong the different sets of serial data “dsx,” “ds1,” and “ds2”outputted from the de-interleave circuits 31, 31 a, and 31 b,respectively, for output to the MAC section 50. Furthermore, the datareception apparatus 2 d is provided with an input section 51 thatcontrols the switching of the selection switch SW. In other respects,the data reception apparatus 2 d of this embodiment is provided with thesame blocks as those provided in the data reception apparatus 2 a (FIG.2) of the first embodiment.

[0082] In the data reception apparatus 2 d configured as describedabove, the RF circuits 22 a and 22 b, quadrature detection circuits 23 aand 23 b, serial-to-parallel conversion circuits 24 a and 24 b, andFourier transform circuits 25 a and 25 b operate in the same manner asin the first embodiment. Moreover, in the subcarrierselection/demodulation circuit 26 d, the channel evaluation circuits 27a and 27 b, channel correction circuits 28 a and 28 b, data selectioncircuit 29, de-mapping circuit 30, and de-interleave circuit 31 operatein the same manner as in the first embodiment. Accordingly,high-frequency signals “S1” and “S2” received via the antennas 21 a and21 b are converted into parallel data “dp1” and “dp2,” then, for eachsubcarrier, the data in good condition is selected to generate paralleldata “dpx,” and then, on the basis of this parallel data “dpx,” serialdata “dsx” is generated.

[0083] The de-mapping circuit 30 a receives the parallel data “dp1” thathas been corrected with respect to each subcarrier by the channelcorrection circuit 28 a. The de-mapping circuit 30 a performs de-mappingon this parallel data “dp1” for each subcarrier, and then feeds theresult to the de-interleave circuit 31 a. The de-interleave circuit 31 aperforms de-interleaving on the parallel data “dp1” demodulated by thede-mapping circuit 30 a to generate serial data “ds1.”

[0084] The de-mapping circuit 30 b receives the parallel data “dp2” thathas been corrected with respect to each subcarrier by the channelcorrection circuit 28 b. The de-mapping circuit 30 b performs de-mappingon this parallel data “dp2” for each subcarrier, and then feeds theresult to the de-interleave circuit 31 b. The de-interleave circuit 31 bperforms de-interleaving on the parallel data “dp2” demodulated by thede-mapping circuit 30 b to generate serial data “ds2.”

[0085] Then, the serial data “dsx,” “ds1,” and “ds2” outputted from thede-interleave circuits 31, 31 a, and 31 b is fed to the contacts “a,”“b,” and “c” of the selection switch SW. At this time, a control signalis fed to the selection switch SW according to how the input section 51is operated so that one of the contacts “a,” “b,” and “c” is connectedto the contact “d” at a time. Specifically, when communication is beingperformed in both the 2.4 GHz and 5.2 GHz frequency bands, the contact“a” of the selection switch SW is selected; when communication is beingperformed in the 2.4 GHz frequency band only, the contact “b” of theselection switch SW is selected; and, when communication is beingperformed in the 5.2 GHz frequency band only, the contact “c” of theselection switch SW is selected.

[0086] Accordingly, when communication is being performed in both the2.4 GHz and 5.2 GHz frequency bands, the serial data “dsx” from thede-interleave circuit 31 is fed through the selection switch SW to theMAC section 50; when communication is being performed in the 2.4 GHzfrequency band only, the serial data “ds1” from the de-interleavecircuit 31 a is fed through the selection switch SW to the MAC section50; and, when communication is being performed in the 5.2 GHz frequencyband only, the serial data “ds2” from the de-interleave circuit 31 b isfed through the selection switch SW to the MAC section 50.

[0087] The configuration of this embodiment can be realized byadditionally providing, in a conventional data reception apparatus thatpermits selection between the IEEE802.11a and IEEE802.11b methods, adata selection circuit 29, a de-mapping circuit 30, and a de-interleavecircuit 31, and by using a selector switch SW that permits selection ofone among three signals as a selector switch for selecting among thosedifferent methods. Thus, the data reception apparatus of this embodimentcan be realized more easily than a conventional data reception apparatusthat can receive and demodulate signals in a plurality of frequencybands.

[0088] In this embodiment, the selection switch SW selects among thesignals from de-interleave circuits 31, 31 a, and 31 b. However, it isalso possible, as shown in FIG. 9, to make the selection switch SWselect among the signals from the de-mapping circuit 30, 30 a, and 30 bso that only one de-interleave circuit 31 is needed. Alternatively, itis possible, as shown in FIG. 10, to make the selection switch SW selectamong the signals from the channel correction circuits 28 a and 28 b andthe data selection circuit 29 so that only one de-mapping circuit 30 andonly one de-interleave circuit 31 are needed.

FIFTH EMBODIMENT

[0089] A fifth embodiment of the invention will be described below withreference to the drawings. FIG. 11 is a block diagram showing theinternal configuration of the data reception apparatus used in thewireless communication system of this embodiment. In the data receptionapparatus shown in FIG. 11, such blocks as serve the same purposes as inthe data reception apparatus shown in FIG. 8 are identified with thesame reference numerals, and their detailed explanations will not berepeated.

[0090] In the data reception apparatus 2 e shown in FIG. 11(corresponding to the data reception apparatus 2 shown in FIG. 1), thesubcarrier selection/demodulation circuit 26 e (corresponding to thesubcarrier selection/demodulation circuit 26 shown in FIG. 1), ascompared with the subcarrier selection/demodulation circuit 26 d (FIG.8), is additionally provided with: carrier detection circuits 32 a and32 b that check the reception condition in the 2.4 GHz and 5.2 GHzbands, respectively, as known from the received electric power on thebasis of the parallel data “dp1” and “dp2” outputted from the Fouriertransform circuits 25 a and 25 b, respectively; and an ON/OFF controlcircuit 33 that turns on and off the individual blocks within thesubcarrier selection/demodulation circuit 26 e. The data receptionapparatus 2 e does not include the input section 51 and the selectionswitch SW provided in the fourth embodiments. In other respects, thedata reception apparatus 2 e of this embodiment is provided with thesame blocks as those provided in the data reception apparatus 2 d of thefourth embodiment.

[0091] In the data reception apparatus 2 e configured as describedabove, when the parallel data “dp1” from the Fourier transform circuit25 a is fed to the carrier detection circuit 32 a, for each subcarrier,the received electric power or the like is checked to check thereception condition in the 2.4 GHz frequency band. When the paralleldata “dp2” from the Fourier transform circuit 25 b is fed to the carrierdetection circuit 32 b, for each subcarrier, the received electric poweror the like is checked to check the reception condition in the 5.2 GHzfrequency band.

[0092] Then, the ON/OFF control circuit 33 is notified of the receptioncondition in the 2.4 GHz and 5.2 GHz bands as recognized by the carrierdetection circuits 32 a and 32 b. Then, if the carrier detectioncircuits 32 a and 32 b recognize good reception condition in both the2.4 GHz and 5.2 GHz bands, the ON/OFF control circuit 33 turns off thede-mapping circuits 30 a and 30 b and de-interleave circuits 31 a and 31b, and turns on the channel evaluation circuits 27 a and 27 b, channelcorrection circuits 28 a and 28 b, data selection circuit 29, de-mappingcircuit 30, and de-interleave circuit 31. As a result of this operation,the serial data “dsx” from the de-interleave circuit 31 is outputted tothe MAC section 50.

[0093] If the carrier detection circuits 32 a and 32 b recognize goodreception condition in the 2.4 GHz band but poor reception condition inthe 5.2 GHz band, the ON/OFF control circuit 33 turns off the channelevaluation circuit 27 b, channel correction circuit 28 b, data selectioncircuit 29, de-mapping circuits 30 and 30 b, and de-interleave circuits31 and 31 b, and turns on the channel evaluation circuit 27 a, channelcorrection circuit 28 a, de-mapping circuit 30 a, and de-interleavecircuit 31 a. As a result of this operation, the serial data “ds1” fromthe de-interleave circuit 31 a is outputted to the MAC section 50.

[0094] If the carrier detection circuits 32 a and 32 b recognize poorreception condition in the 2.4 GHz band but good reception condition inthe 5.2 GHz band, the ON/OFF control circuit 33 turns off the channelevaluation circuit 27 a, channel correction circuit 28 a, data selectioncircuit 29, de-mapping circuits 30 and 30 a, and de-interleave circuits31 and 31 a, and turns on the channel evaluation circuit 27 b, channelcorrection circuit 28 b, de-mapping circuit 30 b, and de-interleavecircuit 31 b. As a result of this operation, the serial data “ds2” fromthe de-interleave circuit 31 b is outputted to the MAC section 50.

[0095] With the configuration of this embodiment, it is possible to turnthe individual blocks on and off according to the reception condition inthe individual frequency bands so that only the necessary blocksoperate. This makes it possible to turn the unnecessary blocks off, andthus helps reduce power consumption as compared with the fifthembodiment.

[0096] In this embodiment, it is also possible, as shown in FIG. 12, touse only one de-interleave circuit 31 and feed the parallel data “dpx”,“dp1,” and “dp2” from the de-mapping circuits 30, 30 a, and 30 b to thede-interleave circuit 31. Alternatively, it is possible, as shown inFIG. 13, to use only one de-mapping circuit 30 and only onede-interleave circuit 31 and feed the parallel data “dpx,” “dp1,” and“dp2” from the data selection circuit 29 and the channel correctioncircuits 28 a and 28 b to the de-mapping circuit 30.

[0097] In the fifth and sixth embodiments, the subcarrierselection/demodulation circuit 26 d or 26 e may be provided with, inplace of the data selection circuit 29, a data synthesis circuit 29 a asin the second embodiment. In the embodiments described above, it isassumed that two frequency bands, namely 2.4 GHz and 5.2 GHz frequencybands, are used as the carrier frequency bands. It is, however, alsopossible to use any other frequency bands than the two specificallymentioned above, and even to use three or more frequency bands as thecarrier frequency bands. Moreover, in the data reception apparatus, eachRF circuit may be provided with a diversity antenna consisting of aplurality of antennas so that, for each RF circuit, whichever of theantennas gives good reception condition is selected.

[0098] According to the present invention, it is possible to transmitdata signals containing identical data in different carrier frequencybands. Thus, when those data signals are received, it is possible toselect the data signal in whichever of the carrier frequency bands givesgood reception condition. Moreover, by synthesizing together those datasignals, it is possible to obtain a data signal closer to one receivedin better reception condition. Moreover, in a case where the OFDM methodis used, by selecting good data for each subchannel, it is possible toreduce the influence of frequency-selective fading that tends to affecta particular frequency band. Moreover, in a case where the OFDM methodis used, by synthesizing data for each subchannel, it is possible toreduce the influence of frequency-selective fading that tends to affecta particular frequency band. Moreover, by turning off the blocks thatprocess data signals in a frequency band in which communication is notcurrently being performed, it is possible to reduce the powerconsumption of the wireless communication apparatus as a whole.

1. A wireless communication apparatus comprising: a modulation circuitthat generates a plurality of data signals containing identical dataeach in one of a plurality of carrier frequency bands; and a pluralityof antennas via which the plurality of data signals outputted from themodulation circuit are transmitted each in a corresponding one of theplurality of carrier frequency bands.
 2. The wireless communicationapparatus according to claim 1, wherein the modulation circuitcomprises: a modulator that generates a baseband signal by modulatingthe data by a predetermined modulation method; and a plurality offrequency converters that convert the baseband signal generated by themodulator respectively into the data signals in the correspondingcarrier frequency bands.
 3. The wireless communication apparatusaccording to claim 2, wherein the predetermined modulation method usedby the modulator is an OFDM method.
 4. A wireless communicationapparatus, comprising: a plurality of antennas via which are receiveddata signals each transmitted in one of a plurality of carrier frequencybands; a plurality of frequency conversion circuits that convert thedata signals received respectively via the plurality of antennas into aplurality of baseband signals having an identical frequency; and ademodulation circuit that, based on the plurality of baseband signalsobtained respectively from the plurality of frequency conversioncircuits, checks reception condition in the carrier frequency bandscorresponding respectively to the plurality of data signals and selectsthe baseband signal obtained from the data signal in the carrierfrequency band in which reception condition is found best and that thendemodulates the thus selected baseband signal, wherein the data signalstransmitted respectively in the plurality of carrier frequency bandscontain identical data.
 5. The wireless communication apparatusaccording to claim 4, wherein, when a data signal is being transmittedonly in one carrier frequency band, the modulation circuit demodulates acorresponding baseband signal without selecting from a plurality ofbaseband signals.
 6. A wireless communication apparatus comprising: aplurality of antennas via which are received data signals eachtransmitted in one of a plurality of carrier frequency bands; aplurality of frequency conversion circuits that convert the data signalsreceived respectively via the plurality of antennas into a plurality ofbaseband signals having an identical frequency; and a demodulationcircuit that synthesizes together the plurality of baseband signalsobtained respectively from the plurality of frequency conversioncircuits into a single baseband signal and that then demodulates thethus synthesized baseband signal; wherein the data signals transmittedrespectively in the plurality of carrier frequency bands containidentical data.
 7. The wireless communication apparatus according toclaim 6, wherein, when a data signal is being transmitted only in onecarrier frequency band, the modulation circuit demodulates acorresponding baseband signal without synthesizing together a pluralityof baseband signals.
 8. A wireless communication apparatus comprising: n(where n is an integer equal to or greater than 2) antennas via whichare received data signals modulated by an OFDM modulation method andtransmitted in n carrier frequency bands; n frequency conversioncircuits that convert the data signals received respectively via the nantennas into baseband signals having an identical frequency; n Fouriertransform circuits that, based on the plurality of baseband signalsobtained respectively from the n frequency conversion circuits, generateparallel data containing data segments each relating to one of m (wherem is an integer equal to or greater than 2) subcarriers; n datacorrection circuits that, based on the parallel data fed respectivelyfrom the n Fourier transform circuits, check reception condition of eachof the m subcarriers in the respective carrier frequency bands andaccordingly correct the parallel data; a data selection circuit thatreceives the n sets of parallel data corrected by the n data correctioncircuits and that then, for each of the m subcarriers, recognizes thecarrier frequency band in which reception condition is best and thatthen selects the data in the thus recognized carrier frequency band soas to thereby newly generate parallel data containing m data segments;and a demodulation circuit that converts the parallel data newlygenerated by the data selection circuit into serial data, wherein theparallel data contained in the data signals transmitted respectively inthe plurality of carrier frequency bands contains identical data.
 9. Thewireless communication apparatus according to claim 8, wherein thedemodulation circuit demodulates parallel data selected from n+1 sets ofparallel data including the parallel data corrected by the n datacorrection circuits and the parallel data newly generated by the dataselection circuit.
 10. The wireless communication apparatus according toclaim 9, further comprising: a carrier detector that, based on theparallel data corrected respectively by the n data correction circuits,checks reception condition in the n carrier frequency bands to recognizean unused one of the carrier frequency bands; and an ON/OFF controlcircuit that turns off, among the n data correction circuits, the datacorrection circuit that corrects the parallel data corresponding to thedata signal in the carrier frequency band recognized as being unused bythe carrier detector and that, when only one of the carrier frequencyband is recognized as being used, turns off the data selection circuit.11. A wireless communication apparatus comprising: n (where n is aninteger equal to or greater than 2) antennas via which are received datasignals modulated by an OFDM modulation method and transmitted in ncarrier frequency bands; n frequency conversion circuits that convertthe data signals received respectively via the n antennas into basebandsignals having an identical frequency; n Fourier transform circuitsthat, based on the plurality of baseband signals obtained respectivelyfrom the n frequency conversion circuits, generate parallel datacontaining data segments each relating to one of m (where m is aninteger equal to or greater than 2) subcarriers; n data correctioncircuits that, based on the parallel data fed respectively from the nFourier transform circuits, check reception condition of each of the msubcarriers in the respective carrier frequency bands and accordinglycorrect the parallel data; a data synthesis circuit that receives the nsets of parallel data corrected by the n data correction circuits andthat then, for each of the m subcarriers, synthesizes the data so as tothereby newly generate parallel data containing m data segments; and ademodulation circuit that converts the parallel data newly generated bythe data synthesis circuit into serial data, wherein the parallel datacontained in the data signals transmitted respectively in the pluralityof carrier frequency bands contains identical data.
 12. The wirelesscommunication apparatus according to claim 11, wherein the demodulationcircuit demodulates parallel data selected from n+1 sets of paralleldata including the parallel data corrected by the n data correctioncircuits and the parallel data newly generated by the data synthesiscircuit.
 13. The wireless communication apparatus according to claim 12,further comprising: a carrier detector that, based on the parallel datacorrected respectively by the n data correction circuits, checksreception condition in the n carrier frequency bands to recognize anunused one of the carrier frequency bands; and an ON/OFF control circuitthat turns off, among the n data correction circuits, the datacorrection circuit that corrects the parallel data corresponding to thedata signal in the carrier frequency band recognized as being unused bythe carrier detector and that, when only one of the carrier frequencyband is recognized as being used, turns off the data synthesis circuit.14. A wireless communication apparatus comprising: n (where n is aninteger equal to or greater than 2) antennas via which are received datasignals modulated by an OFDM modulation method and transmitted in ncarrier frequency bands; n frequency conversion circuits that convertthe data signals received respectively via the n antennas into basebandsignals having an identical frequency; n Fourier transform circuitsthat, based on the plurality of baseband signals obtained respectivelyfrom the n frequency conversion circuits, generate parallel datacontaining data segments each relating to one of m (where m is aninteger equal to or greater than 2) subcarriers; a data selectioncircuit that receives the n sets of parallel data obtained from the nFourier transform circuits and that then, for each of the m subcarriers,recognizes the carrier frequency band in which reception condition isbest and that then selects the data in the thus recognized carrierfrequency band so as to thereby newly generate parallel data containingm data segments; a data correction circuit that, based on the paralleldata newly generated by the data selection circuit, checks receptioncondition of each of the m subcarriers in the respective carrierfrequency bands and accordingly correct the parallel data; and ademodulation circuit that converts the parallel data corrected by thedata correction circuit into serial data, wherein the parallel datacontained in the data signals transmitted respectively in the pluralityof carrier frequency bands contains identical data.
 15. A wirelesscommunication system comprising: a data transmission apparatus builtwith a wireless communication apparatus that comprises: a modulationcircuit that generates a plurality of data signals containing identicaldata each in one of a plurality of carrier frequency bands, and aplurality of antennas via which the plurality of data signals outputtedfrom the modulation circuit are transmitted each in a corresponding oneof the plurality of carrier frequency bands; and a data receptionapparatus built with the wireless communication apparatus thatcomprises: a plurality of antennas which receive data signals eachtransmitted in one of a plurality of carrier frequency bands, aplurality of frequency conversion circuits that convert the data signalsreceived respectively via the plurality of antennas into a plurality ofbaseband signals having an identical frequency, and a demodulationcircuit that, based on the plurality of baseband signals obtainedrespectively from the plurality of frequency conversion circuits, checksreception condition in the carrier frequency bands correspondingrespectively to the plurality of data signals and selects the basebandsignal obtained from the data signal in the carrier frequency band inwhich reception condition is found best and that then demodulates thethus selected baseband signal, wherein a plurality of data signalscontaining identical data are transmitted and received in the pluralityof carrier frequency bands.
 16. A wireless communication systemcomprising: a data transmission apparatus built with the wirelesscommunication apparatus that comprises: a modulation circuit thatgenerates a plurality of data signals containing identical data each inone of a plurality of carrier frequency bands, and a plurality ofantennas via which the plurality of data signals outputted from themodulation circuit are transmitted each in a corresponding one of theplurality of carrier frequency bands; and a data reception apparatusbuilt with the wireless communication apparatus that comprises: aplurality of antennas which receive data signals each transmitted in oneof a plurality of carrier frequency bands, a plurality of frequencyconversion circuits that convert the data signals received respectivelyvia the plurality of antennas into a plurality of baseband signalshaving an identical frequency, and a demodulation circuit thatsynthesizes together the plurality of baseband signals obtainedrespectively from the plurality of frequency conversion circuits into asingle baseband signal and that then demodulates the thus synthesizedbaseband signal, wherein a plurality of data signals containingidentical data are transmitted and received in the plurality of carrierfrequency bands.
 17. A wireless communication system comprising: a datatransmission apparatus built with the wireless communication apparatusthat comprises: a predetermined modulation method, used by themodulator, that is an OFDM method; and a data reception apparatus builtwith the wireless communication apparatus that comprises: n (where n isan integer equal to or greater than 2) antennas which receive datasignals modulated by an OFDM modulation method and transmitted in ncarrier frequency bands, n frequency conversion circuits that convertthe data signals received respectively via the n antennas into basebandsignals having an identical frequency, n Fourier transform circuitsthat, based on the plurality of baseband signals obtained respectivelyfrom the n frequency conversion circuits, generate parallel datacontaining data segments each relating to one of m (where m is aninteger equal to or greater than 2) subcarriers, n data correctioncircuits that, based on the parallel data fed respectively from the nFourier transform circuits, check reception condition of each of the msubcarriers in the respective carrier frequency bands and accordinglycorrect the parallel data, a data selection circuit that receives the nsets of parallel data corrected by the n data correction circuits andthat then, for each of the m subcarriers, recognizes the carrierfrequency band in which reception condition is best and that thenselects the data in the thus recognized carrier frequency band so as tothereby newly generate parallel data containing m data segments, and ademodulation circuit that converts the parallel data newly generated bythe data selection circuit into serial data, wherein a plurality of datasignals containing identical data are transmitted and received in theplurality of carrier frequency bands.
 18. A wireless communicationsystem comprising: a data transmission apparatus built with the wirelesscommunication apparatus that comprises: a predetermined modulationmethod, used by the modulator, that is an OFDM method; and a datareception apparatus built with the wireless communication apparatus thatcomprises: n (where n is an integer equal to or greater than 2) antennaswhich receive data signals modulated by an OFDM modulation method andtransmitted in n carrier frequency bands, n frequency conversioncircuits that convert the data signals received respectively via the nantennas into baseband signals having an identical frequency, n Fouriertransform circuits that, based on the plurality of baseband signalsobtained respectively from the n frequency conversion circuits, generateparallel data containing data segments each relating to one of m (wherem is an integer equal to or greater than 2) subcarriers. n datacorrection circuits that, based on the parallel data fed respectivelyfrom the n Fourier transform circuits, check reception condition of eachof the m subcarriers in the respective carrier frequency bands andaccordingly correct the parallel data, a data synthesis circuit thatreceives the n sets of parallel data corrected by the n data correctioncircuits and that then, for each of the m subcarriers, synthesizes thedata so as to thereby newly generate parallel data containing m datasegments, and a demodulation circuit that converts the parallel datanewly generated by the data synthesis circuit into serial data, whereina plurality of data signals containing identical data are transmittedand received in the plurality of carrier frequency bands.
 19. A wirelesscommunication system comprising: a data transmission apparatus builtwith the wireless communication apparatus that comprises: apredetermined modulation method, used by the modulator, that is an OFDMmethod; and a data reception apparatus built with the wirelesscommunication apparatus that comprises: n (where n is an integer equalto or greater than 2) antennas via which are received data signalsmodulated by an OFDM modulation method and transmitted in n carrierfrequency bands, n frequency conversion circuits that convert the datasignals received respectively via the n antennas into baseband signalshaving an identical frequency, n Fourier transform circuits that, basedon the plurality of baseband signals obtained respectively from the nfrequency conversion circuits, generate parallel data containing datasegments each relating to one of m (where m is an integer equal to orgreater than 2) subcarriers, a data selection circuit that receives then sets of parallel data obtained from the n Fourier transform circuitsand that then, for each of the m subcarriers, recognizes the carrierfrequency band in which reception condition is best and that thenselects the data in the thus recognized carrier frequency band so as tothereby newly generate parallel data containing m data segments, a datacorrection circuit that, based on the parallel data newly generated bythe data selection circuit, checks reception condition of each of the msubcarriers in the respective carrier frequency bands and accordinglycorrect the parallel data, and a demodulation circuit that converts theparallel data corrected by the data correction circuit into serial data,wherein a plurality of data signals containing identical data aretransmitted and received in the plurality of carrier frequency bands.